1. Field of the Invention
The present invention relates to an inclination angle measurement apparatus that sends a wave toward a road surface, and measures an angle of inclination of a vehicle with respect to the road surface based on a phase difference between the phases of received waves reflected from the road surface.
2. Description of Related Art
As an apparatus associated with such an inclination angle measurement apparatus, there has been provided an apparatus for automatically adjusting the distance of illumination of a vehicle-mounted projector. This apparatus is provided with an element for outputting a voltage that is a function of the position of the projector, a detector including two sonars disposed at front and rear sides of the vehicle""s body, respectively, and a transducer for outputting a voltage indicating a phase difference between two reflected waves detected by the two sonars, and a comparator for comparing the voltage from the element with that from the detector, and for transmitting an algebraic difference between the two voltages to a driving device for driving an electromechanical system for controlling the angle of inclination of the projector. The detector simultaneously emits two acoustic waves toward a road surface on which the vehicle is traveling by using the two sonars so as to effectively define a difference between the distance between the front side of the vehicle and the road surface and the distance between the rear side of the vehicle and the road surface, detects the heads of the two acoustic waves reflected from the road surface, and then determines the phase difference between the heads of the two acoustic waves and delivers a voltage indicating the phase difference by using the transducer (see Japanese patent application publication (TOKKAISHO) No.56-8727 (line 6 of first column to line 1 of second column and FIGS. 1 and 2), for example).
While the detector of the prior art apparatus determines the phase difference, i.e. time difference between the head of the reflected acoustic wave detected by one of the two sonars and that of the reflected acoustic wave detected by the other sonar and delivers it as the difference between the distance between the front side of the vehicle and the road surface and the distance between the rear side of the vehicle and the road surface, the detector cannot accurately determine the times at which it starts receiving the two reflected acoustic waves, respectively, because each of them has small energy and a long rising time.
The present invention is proposed to solve the above-mentioned problem, and it is therefore an object of the present invention to provide an inclination angle measurement apparatus that can accurately measure an angle of inclination of a vehicle with respect to a road surface based on a phase difference between the phases of received waves.
In accordance with the present invention, there is provided an inclination angle measurement apparatus including a sending/receiving unit for sending a wave toward a road surface and for receiving two waves reflected from the road surface, and an inclination angle calculating unit for calculating an angle of inclination of a vehicle with respect to the road surface based on a phase difference between the phases of the two reflected waves.
As a result, the inclination angle measurement apparatus in accordance with the present invention can accurately measure the angle of inclination of the vehicle with respect to the road surface based on the phase difference between the received waves.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.